1. The Field of the Invention
The present invention relates to methods of deposition of materials to fill a topography on a surface during the manufacture of semiconductor devices. More particularly, the present invention is directed to a method of deposition of materials to fill a topography which includes faceting of openings in situ with deposition of materials to fill the openings during the manufacture of semiconductor devices.
2. The Relevant Technology
In the continuing quest to reduce the minimum feature size of integrated circuits, the aspect ratio, i.e., the ratio of height to width, of structures to be formed has increased. This is the natural result of attempting to fit as many structures as possible within a given area.
High aspect ratios for structures such as contacts and vias present a challenge for deposition techniques.
Contacts and vias are formed by first etching holes or trenches in an etchable layer, usually silicon dioxide. The hole is then cleaned, then filled with deposited conductive material, typically metal such as aluminum or tungsten deposited by sputtering. To decrease contact resistance, a thin layer of titanium may be sputter deposited in the hole before filling with aluminum or tungsten.
FIG. 1 shows a partial cross section of a partially formed semiconductor device having a substrate or underlying layer 12 with an etchable layer 14 thereon in which has been etched a contact hole or via. The result is a surface on substrate 12 including horizontally oriented surface portions 16 and vertically oriented surface portions 18, joined at top corners 20 and bottom corners 22.
In typical sputter deposition, sputtered flux from a target of material to be deposited approaches a surface at various directions D, as shown in FIG. 2. Top corners 20 shield the lower portions of vertically oriented surface portions 18 from some of the sputtered flux, such that a buildup of a deposited film 24 occurs near upper corners 20 as shown in FIG. 2. When an additional deposited film 26 is deposited to fill the rest of the hole, a void 27 is formed in additional deposited film 26 because of the buildup near upper corners 20. Void 27 causes increased resistance in the contact or via structure, and in severe cases can be large enough to prevent reliable contact all together.
One way to decrease the formation of voids such as void 27 is to etch angled surface portions (facets) 28 on upper corners 20, as shown in FIG. 4, prior to filling the hole. Facets 28 allow more of the sputtered flux to reach the lower portions of the hole, resulting in less likelihood of creating a void. Facets 28 are typically etched in a separate step before filling the hole, after which separate step, a clean step may be required. It would thus be an advantage to combine into one process the steps of etching facets 28 and of depositing a material to fill the hole.